Gulbransen Theatrum - Parts / repair

**Ian_W** · 12-08-2007, 05:11 AM

G'day all,

By way of introduction as I'm new - thanks for having me on board.

I'm from near Sydney Aust and am a retired electrician although not an organist I certainly appreciate the skill of others.

I have a friend with a Gulbransen Theatrum that has failed. I have had a look at it and found that the failure is the transformer in the power supply. It appears to me that I havetwo options available to effect a recovery for him and would certainly appreciate any one who can help.

Option 1: Replace the transformer but where do I get one? Perhaps someone has an organ that has been de-commissioned and would part with the transformer or power supply.

Option 2: Have a replacement transformer built. For this I will need some information. The primary is 240 volts which has a tapping my guess is 110 volts that is wired to the same plug as the power switch. From the marking on the power suply pc board the two secondary windings are 25 and 50 volts. I have no idea of the loadings except that it is protected by a 1 amp fuse.

Regards Ian

**jimmywilliams** · 12-09-2007, 02:49 PM

For Gulbransen parts and service - Daves'electronics here in the US

Gulbransen (All Pre-1986 Models: Parts, Service and Owners Manuals and Tech Support)
Dave's Electronics
105A East Penn St.
Hoopeston, IL 60942
Phone: 217-283-5010
Fax: 217-283-5161
daveelec@cooketech.net
tech support; George Reynertson geojudy@cell1net.net

You may have to send the entire PS unit over there for servicing, or, if you are certain it is the transformer, maybe they have one they can send over to you. Be sure to mention it is the 240v model. THey also sell the service manuals/schematics so this may also help.

You can write directly to George (he is widely known to be the expert onthe earlyGulbransens) but don't ask for him directly if you call the shop..

Transformers rarely fail for no reason. If there was no known cause for the failure (some catastrophic damage) then the entire PS unit should be looked at very closely. Bad power supply filter capacitors can take a transformer down so you should replace those is you haven't done so already. I would be curious to know what the syptoms were before the organ stopped working. If the user reported that there was loud humming then the filter caps probably failed and took down the transformer.

Looking at my schematic (remember mine is the US version)- The power supply unit, looking at it as a whole, should produce the following voltages for the organ: +17, +20, +25, -35, +35DC, as well as 13v AC. The +20 and +25 DC are regulated; the rest are not from what I can tell (I'm certainly no expert!). Part numbers for your reference PS assembly: 413014. Rectifier board 413011, Voltage regulator board: 413003. There are several large value filter cap values used in this unit:5000/32, 4500/20, 2500/20 among them.

I would contact Dave's and see if the replacement transformer is available and if so you should also replace all the filter caps just to be sure.